Mehdi Karroubi at a news conference in 2004, before he fell foul of the Iranian government and was subjected to house arrest.
Photograph: Damir Sagolj/Reuters

An ailing 79-year-old Iranian opposition leader who has been under house arrest since February 2011 has embarked on a hunger strike, demanding authorities try him in public.

Mehdi Karroubi, a former presidential candidate, fell foul of the establishment following the disputed re-election of Mahmoud Ahmadinejad in 2009, which led to months of unrest.

A leader of the Green movement, he was put under round-the-clock surveillance by guards living in his home six years ago, without being put on trial or publicly charged. He has been taken to hospital twice in the last three weeks and has undergone heart surgery.

Saham News, a website close to Karroubi, quoted his wife as saying that he started the dry hunger strike soon after performing his morning prayers on Wednesday, and that he will refuse to eat or drink until his demands are met.

“He wants the security guards to leave the premises of his house,” she said. “Never before – pre-Islamic revolution nor after it – we have seen such presence of guards, living inside the house alongside those under house arrest, keeping all aspects of his life under watch, through bugs and cameras.

“If the house arrest is to continue, he wants to be put on trial in public, after six and a half years under house arrest, he wants the authorities to announce when they will hold a trial in public.”

Two other opposition leaders, Mir Hossein Mousavi, also a former presidential candidate, and his wife, Zahra Rahnavard, were put under house arrest in Tehran in similar circumstances in 2011.

Both Karroubi and Mousavi are suffering from medical complications partly as a result of their age. Mousavi, 75, has also been taken to hospital a number of times in recent years. Some members of the three leaders’ immediate families are allowed to visit them in pre-arranged and approved meetings.

“My father wants a trial that is held in public and in the presence of a jury as provisioned by article 168 of the constitution,” Karroubi’s son, Mohammad-Taghi Karroubi, said. “The establishment wants a quiet end to the house arrests, without paying a price. My father has said that he will not challenge the verdict of a trial, he hasn’t had a chance to defend himself and he wants to respond to the accusations made by the state.”

He said he had spoken to his father by phone recently when he was discharged from hospital. It was the first time in six months the two had been allowed to talk. “My father is on the verge of becoming 80 and a dry hunger strike, which given his health complications raises serious concerns.”

The continued restrictions on opposition leaders is a major challenge for the moderate president, Hassan Rouhani, and popular demand for an end to the house arrests is high. Almost every rally Rouhani held during the campaign that led to his re-election in May featured chants by supporters in support of Karroubi, Mousavi and Rahnavard.

Karroubi’s recent medical problems have prompted renewed pleas for his release. A number of activists and supporters tried to visit him in hospital, but were prevented from doing so. Pictures surfaced online of activists expressing sympathy with his wife outside the hospital.

One image showed Karroubi in his hospital bed with his wife at his side, and with flowers sent on behalf of Mousavi and Rahnavard.

Karroubi, who was imprisoned before the Islamic revolution in 1979, told the Guardian in a rare 2010 interview that despite widespread corruption, the shah treated his opponents less harshly than the regime at the time.

Amnesty International also expressed concern on Wednesday about the health of an incarcerated Iranian human rights defender, Arash Sadeghi, who it said was critically ill. Sadeghi, 30, suffers from deteriorating digestive and respiratory problems. “The denial of access to medical care in these circumstances amounts to torture,” it said.